Stacking Mode-Driven Enhancement of Optoelectronic and Electrocatalytic Properties in Bilayer 2H MoS.

The stacking orientation of bilayer two-dimensional (2D) materials introduces an additional degree of freedom that can profoundly influence their electronic, optoelectronic, and electrochemical properties. While stacking-engineered phenomena such as ferroelectricity, superconductivity, and second harmonic generation have been widely studied in bilayer molybdenum disulfide (MoS), their impact on functional device performance, particularly photoresponse and electrocatalysis, remains largely unexplored. Here, we investigate how the stacking configuration governs the optoelectronic and electrocatalytic behavior of bilayer MoS, focusing on the two stable stacking orders: 2H and 3R synthesized via chemical vapor deposition (CVD). Photodetection measurements reveal that 2H stacked bilayer MoS exhibits a remarkable two-orders-of-magnitude enhancement in photoresponsivity over its 3R counterpart, attributed to stronger interlayer coupling and more efficient charge transfer. Additionally, 2H MoS demonstrates enhanced field-effect transistor (FET) characteristics and achieves twice the hydrogen evolution reaction (HER) activity compared to 3R MoS. We employ scanning electrochemical cell microscopy (SECCM) to achieve spatially resolved mapping of electrocatalytic reactivity, offering the first direct nanoscale visualization of stacking-dependent HER activity. These findings underscore the crucial role of stacking orientation of atomic layers in tuning both optoelectronic and electrocatalytic properties, paving the way for stacking-engineered 2D materials in next-generation photodetectors and electrocatalytic devices.